One of the pictures posted by ISIS that appear to show militants taking captured Iraqi soldiers to be executed

Militants from the Islamic State in Iraq and Syria, or ISIS, claimed they executed 1,700 Iraqi government soldiers and posted horrific photos on Twitter to support their allegations. The pictures, which were released at a time when, according to the Washington Post "a semblance of normality" was returning to Baghdad, show how masked men load young men into flatbed trucks to take them to a shallow ditch, where they are apparently shot. There is no way to verify the claim by the insurgents that they killed so many soldiers but the New York Timespoints out that if the claim is true, “it would be the worst mass atrocity in either Syria or Iraq in recent years, surpassing even the chemical weapons attacks in the Syrian suburbs of Damascus last year, which killed 1,400 people and were attributed to the Syrian government.”

Some are skeptical. “We’re trying to verify the pics, and I am not convinced they are authentic,” said Erin Evers, Human Rights Watch researcher in Iraq. But the Associated Press talks to Iraq’s top military spokesman, who confirmed the authenticity of the photos, saying he had heard of mass murder of captured Iraqi soldiers in areas controlled by the ISIL. He doesn’t, however, confirm the claim of the number of soldiers killed. Most of those in the pictures are in civilian clothes, suggesting the ISIS captured soldiers as they were trying to escape, notes reporter Jenan Moussa on Twitter. Indeed, one of the pictures shows a soldier wearing civilian clothes over his uniform.

The photographs show the militants with lots of U.S.-supplied material, details the Long War Journal. The ISIS posts pictures of lots of U.S. vehicles, including Humvees and Ford and Chevy pickup trucks. Other photographs show the ISIS militants holding U.S.-made M-16 assault rifles, which were the weapons that had been issued to the Iraqi security forces. Some of the pictures appear to show Iraqi soldiers pleading for their lives before they’re forced to lie face-down in shallow ditches with their hands behind their backs. The final pictures show the bodies of the captives soaked in blood.

A selection of the pictures is posted after the jump. Needless to say, they are extremely graphic. All the photographs are available here.

Daniel Politi has been contributing to Slate since 2004 and wrote the "Today's Papers" column from 2006 to 2009. You can follow him on Twitter @dpoliti.